This invention relates to a data backup apparatus for backing up data by controlling power fed to a memory, and a step-up/down power supply for feeding power to on-vehicle equipments, e.g., a car navigation device, and so on.
In a conventional data backup apparatus, an SRAM, a rewritable ROM or the like is installed therein, and data in an on-vehicle equipment such as a car navigation device is saved in the SRAM or the like.
However, in the case of using an SRAM, the limited amount of storable information per area makes it difficult to save a large amount of data.
In addition, in the case of using a rewritable ROM, a considerable time is required for information rewriting, and due to its inherent characteristics, a limit is placed on the number of rewritable times. Thus, in general, data saving by use of a ROM has been limited to a program code and so on, which requires no rewriting operation, and work information has not been saved at all.
Therefore, it was required to save only minimum necessary information in the SRAM and read other data from an external memory or the like at the time of starting the on-vehicle equipment, thereby to restructure the data in a main memory.
Since the conventional data backup apparatus is constructed as mentioned above, it requires a large amount of data, such as map information on the surroundings, to be read from an external memory or the like, at the time of starting the on-vehicle equipment. Thus, there has been such an inevitable problem in the conventional art that a considerable time is required before the on-vehicle equipment starts its actual operation.
The installation of a large-capacity SRAM eliminates the necessity of reading a large amount of data from an external memory at the time of starting the on-vehicle equipment. However, because of the limited amount of storable information per area and the high price of an SRAM, it is not practical to install a large-capacity SRAM in an on-vehicle equipment.
The present invention has been made to solve the foregoing problems, and it is an object of the invention to provide a data backup apparatus capable of saving a large amount of data inside an on-vehicle equipment.
It is another object of the invention to provide a step-up/down power supply capable of stably operating an on-vehicle equipment by applying a predetermined voltage to the on-vehicle equipment even when fluctuation occurs in a voltage applied from a main power supply such as an on-vehicle battery.
In accordance with the present invention, there is provided a data backup apparatus, comprising: control means for changing a dynamic RAM to a self-refresh mode when detection means detects an OFF command of a main power supply, and feeding power from a backup power supply to the dynamic RAM.
Thus, it is possible to save a large amount of data inside an on-vehicle equipment.
According to the data backup apparatus of the invention, power is fed from the main power supply to the dynamic RAM during the period from the detection of the OFF command of the main power supply to the completion of the changing to the self-refresh mode.
Thus, it is possible to surely save the data of the on-vehicle equipment.
According to the data backup apparatus of the invention, among a plurality of memory areas constituting the dynamic RAM, a memory area that receives power from the backup power supply is designated, and power is fed only to the thus designated memory area.
Thus, it is possible to reduce power consumption during the backing-up operation.
According to the data backup apparatus of the invention, information regarding the memory area to receive power from the backup power supply is indicated.
Thus, it is possible to verify the normal ending of previous processing, and normal backing-up during the stopped period. It is also possible to verify an unexpected memory loss or the like caused by a reduction in a backup power supply or the like during the backing-up operation.
According to the data backup apparatus of the invention, the feeding of power from the main power supply to a predetermined equipment is stopped, when the output voltage of the main power supply is reduced.
Thus, it is possible to suppress a reduction in the output voltage of the main power supply.
According to the data backup apparatus of the invention, if an SDRAM is used as the dynamic RAM, the control means and the SDRAM are kept separated from each other until the initial setting of the control means is completed.
Thus, it is possible to prevent the destruction or the like of data saved in the SDRAM.
In accordance with the invention, there is provided a step-up/down power supply, comprising: a step-up DC/DC converter for outputting a predetermined voltage by stepping up a voltage applied from a main power supply when the applied voltage drops below a reference voltage.
Thus, since the predetermined voltage can be applied to an on-vehicle equipment even if a cranking operation or the like causes a reduction in the voltage applied from the main power supply, it is possible to stably operate the on-vehicle equipment.
According to the step-up/down power supply of the invention, a voltage signal is captured from an outputting stage for outputting a predetermined voltage, so as to activate a switching element of the step-up DC/DC converter.
Thus, even if the voltage applied from the main power supply drops below the operating voltage of the switching device, it is possible to continue the operation of the step-up DC/DC converter.